1. Field of the Invention
The invention relates to an image forming apparatus with an electrode unit having a plurality of apertures for use in a copying machine, a printer, a plotter, a facsimile machine, or other apparatus that produces a printed product.
2. Description of the Related Art
Heretofore, there has conventionally proposed an image forming apparatus in which an image is formed by using a plurality of apertures. In this image forming apparatus, a voltage is selectively applied to the apertures in accordance with image data to control toner particles to selectively pass through the apertures. The toner particles which could pass through the apertures form an image on an image forming medium. This type of an image forming apparatus is disclosed in U.S. Pat. No. 3,689,935.
This image forming apparatus includes an aperture electrode having a plain plate made of an insulating material, a continuous reference electrode formed on a one side of the plain plate and a segmented control electrode formed on the other side of the plain plate. The electrodes of the segmented control electrode are insulated from each other. The aperture electrode is formed as at least one row of apertures through the three layers with an aperture through each electrode of the segmented control electrode. The image forming apparatus further comprises a power supply for supplying an electric potential selectively between the reference electrode and the electrodes of the segmented control electrode, a toner supplier for supplying toner particles so that the density of the particle stream is modulated according to the pattern of potentials applied to the electrodes of the segmented control electrode, and positioning means for positioning a print receiving medium in the particle stream by moving the print receiving medium and the aperture electrode relatively.
However, this conventional apparatus does not provide high speed printing and further reduces printing quality by blinding the apertures.
The applicant proposed an improved version of the image forming apparatus in patent application Ser. No. 08/112,471 filed on Aug. 27, 1993 by the same inventor. application Ser. No. 08/112,471 improves a printing characteristic by contacting an aperture electrode with a toner carry means having toner. In this apparatus, toner particles are supplied concurrently with the contacting toner around the apertures of the aperture electrode so that toner which can cause blinding of the apertures does not accumulate on the apertures. Consequently the apertures of the aperture electrode aren't blinded.
In application Ser. No. 08/112,471, a force is added to the toner on the toner carrier means by rubbing the toner on the toner carrier means with the aperture electrode. Consequently, the distribution and adhesion of the supplied toner on the toner carrier means is not uniform either to charge or thickness because of imperfections, however slight, in the toner carrier means. Therefore, the toner having a slight or lesser charge and the toner being fully charged are mixed and supplied concurrently. A switching potential difference, which is the difference between the control voltage at off time when all of the toner particles are retained on the toner carrier means and the control voltage at on time when the necessary toner particles flow to the print receiving medium, must increase to compensate for this inequality in charge. Consequently, expensive driving elements are required. Further, the toner given the unequal charges flows in greater amounts to the image forming part thereby producing an excessive or dirty image.